The U.S. Food and Drug Administration and the Centers for Disease Control and Prevention are widening their investigation into a cyclosporiasis outbreak linked to shredded iceberg lettuce from central Mexico after identifying cases in four additional states.

US officials claim evidence points to lettuce grown in Mexico, which Mexico's Health Ministry disputes.

CDC confirms 4,173 U.S. Cyclospora cases as it investigates a lettuce-linked outbreak. More than 7,400 additional reports remain under review.

Investigators believe additional states will help them better construct how cyclosporiasis moved through the nation's food supply.